Economic triac control. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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Electrical appliances with pulsed power consumption (energy-saving lamps, household appliances with pulsed power supplies) that have entered our everyday life place new demands on electronic switches based on triacs.
If to turn on the active load (incandescent lamps, electric heaters) it was enough to apply a short opening pulse at the beginning of the half-cycle to the control electrode of the triac, then to turn on the load with non-linear consumption, it is necessary to pass current through the control electrode of the triac during the entire half-cycle.
The control current can be quite large (up to 200 mA for KU208N), and this fact seriously affects the efficiency and dimensions of the device switching the load. The question arises, is it possible to make the control current do something else, for example, power the rest of the device?
An example of such a solution is the triac control circuit shown in the figure.
The value of the triac control current VS1 is determined by the capacitance of the capacitor C1, which, unlike a resistor, does not dissipate power. The phase of this current is shifted with respect to the phase of the mains voltage by 90о, i.e., its value is maximum when the mains voltage passes through zero, which keeps the triac open at low currents less than the holding current.
Thus, the triac clearly opens at the beginning of the half-cycle when working with both low-power and non-linear loads. In addition, the same control current, passing through a rectifier assembled on diodes VD1, VD4, and a stabilizer on zener diodes VD2, VD3 is used to power the rest of the device.
You can control the load by applying a voltage log for a short time. 1 to the input R (disable) or S (enable) of the trigger DD1.1 or by setting the corresponding signal at input D. The load switching in the latter case will be carried out at input C. Transistors VT1, VT2 in the open state shunt the triac control circuit, diverting through themselves control current. The power supply circuit of the low-voltage stabilizer is not interrupted.
Resistor R1 smooths out current surges when the device is connected to the network. Resistors R2, R3 limit the base currents of transistors VT1, VT2.
Part numbers are not critical. The capacitance of the capacitor C1 should be selected from the condition of the allowable current through the control electrode of the triac VS1 and the current consumption of the low-voltage part of the device. Zener diodes VD2, VD3 - for half the supply voltage of the low-voltage part. The capacitance of capacitors C2 and C3 is 470 ... 1000 uF, the rated voltage is not lower than the stabilization voltage of the zener diodes. Transistors VT1, VT2 - any low-power corresponding structures with a static current transfer coefficient of the base h213 of at least 100.
Author: A. Dzanaev
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